An imaging apparatus called an amplifying type MOS sensor is used in an electronic video camera or an electronic still camera. In recent years, in association with the realization of advanced functions of those imaging apparatuses, an imaging apparatus having what is called an electronic zooming function for magnifying or reducing an image by outputting a signal only from a desired region in an imaging region has appeared.
As an imaging apparatus having the electronic zooming function, there is an imaging apparatus disclosed in Japanese Patent Application Laid-Open No. 2007-074032. It is an object of Japanese Patent Application Laid-Open No. 2007-074032 to prevent the occurrence of a difference of accumulation time and to keep quality of an output image even when an electronic zoom magnification is changed at the time of photographing a moving image, that is, even in the case where a drive mode of the imaging apparatus is switched.
A request for low costs of the imaging apparatus is strong and miniaturization of the imaging apparatus is demanded. As a technique for realizing the miniaturization of the imaging apparatus, there is an amplifying type MOS sensor having what is called a 3-transistor construction, disclosed in Japanese Patent Application Laid-Open No. 2003-046864, in order to assure an area of a photodiode by decreasing an area of a transistor which occupies per pixel.
In the amplifying type MOS sensor disclosed in Japanese Patent Application Laid-Open No. 2003-046864, having the 3-transistor construction which does not include a selection MOS transistor, an electric potential corresponding to the reset electric potential appears in a vertical output line when charges accumulated in a photodiode (PD) are reset. Therefore, timing for resetting the charges accumulated in the PD in a selection row by a reset scan (hereinbelow, reset row) and timing for reading out the charges accumulated in the PD in the selection row by a read out scan (hereinbelow, read out row) to an accumulation capacitor provided at the subsequent stage of the vertical output line cannot be performed concurrently.
In the imaging apparatus disclosed in Japanese Patent Application Laid-Open No. 2007-074032, since the scan of the read out row and the scan of the reset row are not overlapped, the electronic zoom magnification can be changed even in the amplifying type MOS sensor with the 3-transistor construction.
However, there is a case where it is required to variably change the accumulation time depending on a photographing condition such as luminance or the like of an object. For example, it is preferable to extend the accumulation time when the luminance of the object is low. However, in the imaging apparatus disclosed in Japanese Patent Application Laid-Open No. 2007-074032, since the scan of the reset row is started only after completion of the read out scan, a range where the accumulation time can be adjusted is limited. Further, when a frame rate rises, a time that is required until the start of the read out scan of the following frame after completion of the read out scan becomes short and an interval from the reset row scan to the read out scan, that is, a time which can be used as an accumulation time becomes short. There is, consequently, a risk of occurrence of such a situation that the necessary accumulation time cannot be assured. If a gain is corrected in order to compensate a lack of light amount that is caused due to the shortening of the accumulation time of the frame just after the drive mode is switched, a deterioration in picture quality is caused.